PROJECT ABSTRACT In response to RFA-MH-19-120, the goal of this study is to validate the effectiveness of a new automated online screening tool?the Social Communication (SoCo) CheckUp?that incorporates empirically-tested screening items for communication delay and autism spectrum disorder (ASD) in 3-month age intervals. This new screening tool is designed for universal screening at well-child visits at 9, 12, 15, 18, 21, and 24 months of age to screen for communication delay and autism. The SoCo CheckUp is part of our Baby Navigator portal, a new mobile application that includes the SoCo Growth Charts?a developmental surveillance for families to answer questions about SoCo milestones every 2 months to chart their child?s growth in 5 domains and to explore hundreds of video clips illustrating early milestones with narration on responsive parenting. Families with a positive autism screen have links to three ASD-specific tools. We will recruit 4,000 infants by 2 months of age at one of their first well child visits and invite families to the SoCo Growth Charts for developmental surveillance. We will then invite families into the portal to screen with the SoCo Checkup based on parent report at 9 months, with repeat screenings at 12, 15, 18, 21, and 24 months. All families of children with a positive autism screen on the SoCo Checkup and a comparable number of children with a negative screen will be invited to collect home observations for an observational screener using the Systematic Observation of Red Flags of ASD (SORF) at the same ages from 9-24 months. All children with a positive ASD screen on the SORF and a comparable number of children randomly select with a negative SORF screen will be invited for a confirmatory diagnostic evaluation at 24 months. We anticipate confirming ASD for least 80 children based on previous research detecting 1/50. We will address the following research aims: Aim 1. Study psychometric features of the SoCo Checkup cut- off and composite to diagnostic outcome; Aim 2. Study the trajectories of the SoCo surveillance and screening to predict autism symptom severity; and Aim 3. Construct a risk algorithm based on multiple parameters to develop an efficient, cost-effective mobile screening application for use in infants that is readily deployable in the general population. The expected outcomes of this validation study will demonstrate the effectiveness of an online surveillance and screening system beginning in the first year of life that will be ready for immediate, rapid, scalable, and sustainable deployment across the US. Findings will advance science by providing researchers with a method for recruiting a community sample, allowing for research at younger ages, which could accelerate genetic, biomedical, and intervention research. The use of innovative technology, user-friendly tools and web- applications, and implementation science methodology enhances the potential for sustainability and scalability that can lead to transformative changes to efficiently and effectively screen infants for communication delay and autism and improve healthcare delivery.